Process of making composite glass



W. IOWEN PhocEss OF MAKING cokrbsfln GLASS July 29, 1930.

Filed Nbv. 2. 192a INVENTOR WWW Patented July 29; 1930 UNITED STATES PATENT OFFICE I WILLIAM OWEN, F PITTSBURGH, PENNSYLVANIA, .ASSIGNOR 1'0 PITTSBURGH PLATE- GLASS OO IYANY, A. GORPQBATIQN O1 PENNSYLVANIA PBlOOESS OF HAKI IING COMPOSITE GLASS Application med November 2, 1923. Serial no. 816,701..

The invention relates to a process of making composite glass, and particularl to the procedure whereby the separation 0 the edges of the sheets making up the composite plates is 5 avoided. Composite glass is formed by cementing to the opposite sides of a sheet of pyroxylin plastic;such as celluloid or pyralin, a pair of glass sheets, the cement employed being ordinarily gelatin. A film of gelatin is dried upon the face of each of the glass sheets, and after the pyralin is placed therebetween, heat and pressure are applied to soften the gelatin and secure proper adhesion, the composite plate thus formed being kept under pressure during the heating operation. The heating and pressing operations are either carried on in rubber containers placed in a pressure tank, or the assembled sheets are placed between the steam heated platens of a hydraulic press. The sheets of glass and pyralin are cut'to substantially exact size before compositing, so that the composited plate merely requires that its edges be smoothed up in order to-make it a complete finished product ready for use.

Composite plates, as thus produced, de-

l velop a tendency to separate or let go at the edges. That is the cement will, in a number of cases, let go at certain points along the 3 edges, so that the glass shows a loss of transparency at such points, which in the course of time spreads inward and may require the re lacement of the plate. To avoid this troufile, it has been customary to groove out the gyralin along the edges of the plate to the epth of an eighth 0 an inch or more, and fill the groove with pitch or other sealing ma-,

terial. This expedient is expensive,'mars the appearance of the product somewhat, and is 40 not, in all cases, efiective in preventing the let go or, separating.

I have found a means of entirely overcoming this separation without employing the sealing operation. Instead of cutting the sheets to approximately finished size, as'has heretofore been done, they are cut oversize, ordinarilyabout one inch greater in length and width than the plate to be produced. he sheets are then composited in the usual way, and the plate thus produced, is trimmed down showingthe saws or disc's cutting through the to exact size by the use of an abrading wheel which acts as a saw. The practice of the invvention is illustrated in the accompanying drawings, wherein:

Figure 1 is a perspective view of a sheet of composite glass preliminary to the step of cutting the stripsfrom the edgesto bring it to exact size. And Fig. 2 is a sectional view i composite sheet to trim it to size.

Referring to the drawings, the sheets 1, 2 and 3 comprise the composite plate, 1 and 2 being glass'sheets cemented 'to the celluloid or pyralin sheet 3 as heretofore descibed. These sheets are oversize about one inch, so that there is a margin to be cut off each edge about one-half inch in width, the dotted lines 4;, 4; and 5, 5 indicating the lines along which the plate must be'trimmed to bring it'to exact size. v

The edges are preferably cut or sawed ofiby the use of the cutting wheels or discs as indicated in Fig. '2. These discs are referably made of a bakelite base with car orun-.

dum particles embedded therein, such wheels having the necessary strength and wearing qualities. They are relatively thin and are rotated at a high rate of speed. The wheels are set so that their cuts overlap, each wheel cutting through one glass sheet and the pyralin sheet. The plate is carried upon a suitable table (not shown), to which it is secured, and means are provided for feedin the plate between the wheels at a rate upwar s of twenty-four inches a minute, depending on the thickness of the plate and the speed of rotation of the wheels.

I have found, as heretofore indicated, that plates composited in this manner do not de-- velop separations or let goes at their edges and require .no sealing. The cost of sawing ofi the edges is a small consideratiomin view of the improved product secured by the practice of the process, and in view of the avoidance ofthe requirement for sealing the edges. The surfaces left by the sawing operation are relatively smooth and true so that-the labor involved in finishing these edgesis relatively slight;

What I claim is: I.

1. A rocess of making a com osite glassplate v definite predetermined 'menslons, which consists in attaching a pair of' lass sheets to the opposite sides of a sheet 0 py roxylin plastic by the application of heat and. pressure, using sheets having over all dimensions greater than said predetermined dimensions, and then cutting strips 01f all of the edges of the plate thus formed to bring the plate to said predetermined dimensions.

2. A process of making a composite glass plate of definite predetermined dimensions, which consists in attaching a pair of glass sheets to the opposite sides of a sheet of pyroxylin plastic by the application of heat and pressure, using sheets having over all dimensions greater than said predetermined dimensions, and then sawing strips off all of the edges of the plate thus formed to bring the plate to said predetermined dimensions.

In testimony where0f, 1 have hereunto subscribed my name this 15th day of Oct., 1928.

' WILLIAM OWEN. 

